JP2016025716A - Nonaqueous electrolyte secondary battery system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide means for further increasing cycle durability against hundreds of cycles, which is required in the case of using, as a power source for an electric motor vehicle, a nonaqueous electrolyte secondary battery arranged in the form of a laminate battery having an electrolytic solution containing an electrode protectant.SOLUTION: A nonaqueous electrolyte secondary battery system comprises: a nonaqueous electrolyte secondary battery arranged by sealing, in an outer sheath, a power-generating element having unit cell layers each including a positive electrode including a positive electrode collector and a positive electrode active material layer formed on the surface of the positive electrode collector, a negative electrode including a negative electrode collector and a negative electrode active material layer formed on the surface of the negative electrode collector, and a separator for holding an electrolytic solution together with the electrolytic solution containing an electrode protectant so that an excess space is present in the outer sheath; pressure-applying means for applying an external pressure to the nonaqueous electrolyte secondary battery; SOC-calculation means for calculating SOC of the nonaqueous electrolyte secondary battery; and control means for controlling the pressure-applying means based on SOC calculated by the SOC calculation means to regulate the external pressure. The control means lowers the external pressure when the SOC reaches a predetermined value or less in discharging the nonaqueous electrolyte secondary battery.SELECTED DRAWING: Figure 5

Description

  The present invention relates to a non-aqueous electrolyte secondary battery system.

  In recent years, the development of electric vehicles (EV), hybrid electric vehicles (HEV), and fuel cell vehicles (FCV) has been promoted against the background of the increasing environmental protection movement. A secondary battery that can be repeatedly charged and discharged is suitable as a power source for driving these motors, and a non-aqueous electrolyte secondary battery such as a lithium ion secondary battery that can be expected to have a high capacity and a high output is attracting attention.

The power generation element of the nonaqueous electrolyte secondary battery has a positive electrode active material layer containing a positive electrode active material (for example, LiCoO ₂ , LiMnO ₂ , LiNiO _2, etc.) formed on the current collector surface. The power generation element of the non-aqueous electrolyte secondary battery includes a negative electrode active material (for example, carbonaceous materials such as metallic lithium, coke and natural / artificial graphite, metals such as Sn, Si, and the like) A negative electrode active material layer including an oxide material or the like. The positive electrode active material layer and the negative electrode active material layer are usually laminated via a separator for holding an electrolyte such as a liquid electrolyte, thereby forming a power generation element of a nonaqueous electrolyte secondary battery. . This power generation element is usually enclosed in an exterior material such as an aluminum laminate film together with a liquid electrolyte, and sealed in a vacuum to complete a battery (see, for example, Patent Document 1).

JP 2005-339931 A

  According to the study by the present inventors, the so-called laminate battery as described in Patent Document 1 or the like still has insufficient cycle durability of several hundred cycles required when used as a power source for an electric vehicle. There was found.

  Here, conventionally, a technique for adding an additive (electrode protective agent) such as vinylene carbonate to an electrolytic solution for the purpose of improving the cycle durability of the nonaqueous electrolyte secondary battery is known. Such an electrode protective agent contributes to improving the durability of the battery by forming a SEI film on the surface of the battery, particularly the negative electrode. However, according to the study by the present inventors, it has been found that even when such an electrode protective agent is added to the electrolytic solution, sufficient cycle durability may still not be achieved.

  Therefore, the present invention can further improve the cycle durability of several hundred cycles required when used as a power source for an electric vehicle in a non-aqueous electrolyte secondary battery in the form of a laminated battery in which the electrolytic solution contains an electrode protective agent. It aims to provide a means.

  The present inventors have intensively studied to solve the above problems. In the process, it was found that the cause of the decrease in the cycle durability of the so-called laminated battery is the deterioration of the active material layer in a region where the SOC of the battery is as small as several percent (low SOC region). And based on this knowledge, especially in the low SOC region, it was confirmed that the deterioration of the cycle durability in the laminate battery can be suppressed by effectively suppressing the deterioration of the electrode by using the electrode protective agent. It came to complete.

  That is, the non-aqueous electrolyte secondary battery system according to the present invention calculates the SOC of the non-aqueous electrolyte secondary battery, the pressurizing means for applying external pressure to the non-aqueous electrolyte secondary battery, and the non-aqueous electrolyte secondary battery. And a control means for controlling the pressurizing means to adjust the external pressure based on the SOC calculated by the SOC calculating means. The non-aqueous electrolyte secondary battery includes a positive electrode in which a positive electrode active material layer is formed on the surface of a positive electrode current collector, a negative electrode in which a negative electrode active material layer is formed on the surface of a negative electrode current collector, A power generation element having a single battery layer including a separator for holding a liquid is enclosed inside the exterior body together with an electrolyte containing an electrode protective agent so that an excess space exists inside the exterior body. It will be. In the non-aqueous electrolyte secondary battery system according to the present invention, the control means reduces the external pressure when the SOC becomes a predetermined value or less during discharge of the non-aqueous electrolyte secondary battery. There is a feature in the point.

  According to the nonaqueous electrolyte secondary battery system of the present invention, the external pressure applied to the nonaqueous electrolyte secondary battery is reduced when the SOC of the nonaqueous electrolyte secondary battery becomes a predetermined value or less. As a result, more electrode protective agent moves between the electrodes (between the positive electrode active material layer and the negative electrode active material layer), and deterioration of the active material layer is suppressed by the action of the electrode protective agent. As a result, a decrease in cycle durability in the laminate battery is suppressed, and it is possible to improve the cycle durability of several hundred cycles required when used as a power source for an electric vehicle.

It is a block diagram for demonstrating the structure of the secondary battery system which concerns on one Embodiment of this invention. It is the cross-sectional schematic which represented typically the basic composition of the nonaqueous electrolyte lithium ion secondary battery which is not a flat type (stacked type) bipolar type. It is a perspective view for demonstrating the pressurization apparatus part containing the secondary battery of the secondary battery system to which this invention is applied. It is a side view of the pressurization apparatus part containing a secondary battery. It is a flowchart which shows the control procedure of the secondary battery system which concerns on one Embodiment of this invention.

  One embodiment of the present invention holds a positive electrode in which a positive electrode active material layer is formed on the surface of a positive electrode current collector, a negative electrode in which a negative electrode active material layer is formed on the surface of a negative electrode current collector, and an electrolyte solution. A non-aqueous power generation element having a single battery layer including a separator for sealing with an electrolytic solution containing an electrode protective agent inside the exterior body so that an excess space exists inside the exterior body An electrolyte secondary battery (hereinafter also simply referred to as “secondary battery”), a pressurizing means for applying an external pressure to the nonaqueous electrolyte secondary battery, and an SOC calculation for calculating the SOC of the nonaqueous electrolyte secondary battery And control means for controlling the pressurizing means based on the SOC calculated by the SOC calculating means to adjust the external pressure, wherein the control means discharges the nonaqueous electrolyte secondary battery. At that time, the SOC is below a predetermined value. Wherein the reducing the external pressure to come, a non-aqueous electrolyte secondary battery system (hereinafter, simply referred to as "secondary battery system") is.

  FIG. 1 is a block diagram for explaining a configuration of a secondary battery system according to an embodiment of the present invention. FIG. 2 is a schematic cross-sectional view schematically showing a basic configuration of a non-aqueous electrolyte lithium ion secondary battery that is not a flat type (stacked type) bipolar type. FIG. 3 is a perspective view for explaining a pressure device portion including a secondary battery of a secondary battery system to which the present invention is applied, and FIG. 4 is a side view of the pressure device portion similarly including a secondary battery. is there.

  The secondary battery system of this embodiment includes a secondary battery 10, a pressurizing device 4 (pressurizing means) that pressurizes the secondary battery 10 with the secondary battery 10 interposed therebetween, and a secondary battery using the pressurizing device 4. A controller 3 (control means) that adjusts the external pressure applied to 10 is provided.

  Here, as an example of the secondary battery 10 according to the present embodiment, a non-aqueous electrolyte lithium ion secondary battery that is not a flat (stacked) bipolar type will be described. However, in carrying out the present invention, the secondary battery 10 is not particularly limited as long as it is a nonaqueous electrolyte secondary battery.

  As shown in FIG. 2, the secondary battery 10 of the present embodiment has a structure in which a substantially rectangular power generation element 21 in which a charge / discharge reaction actually proceeds is sealed inside a laminate film 29 that is an exterior body. . Here, the power generation element 21 has a configuration in which a positive electrode, a separator 17, and a negative electrode are stacked. The separator 17 contains a nonaqueous electrolyte (for example, a liquid electrolyte). The positive electrode has a structure in which the positive electrode active material layer 13 is disposed on both surfaces of the positive electrode current collector 11. The negative electrode has a structure in which the negative electrode active material layers 15 are disposed on both surfaces of the negative electrode current collector 12. Specifically, the negative electrode, the electrolyte layer, and the positive electrode are laminated in this order so that one positive electrode active material layer 13 and the negative electrode active material layer 15 adjacent thereto face each other with a separator 17 therebetween. Thereby, the adjacent positive electrode, electrolyte layer, and negative electrode constitute one unit cell layer 19. Therefore, it can be said that the stacked battery 10 shown in FIG. 2 has a configuration in which a plurality of single battery layers 19 are stacked and electrically connected in parallel.

  In addition, although the positive electrode active material layer 13 is arrange | positioned only at one side in the outermost layer positive electrode collector located in both outermost layers of the electric power generation element 21, an active material layer may be provided in both surfaces. That is, instead of using a current collector dedicated to the outermost layer provided with an active material layer only on one side, a current collector having an active material layer on both sides may be used as it is as an outermost current collector. In addition, the arrangement of the positive electrode and the negative electrode is reversed from that in FIG. 2 so that the outermost negative electrode current collector is positioned on both outermost layers of the power generation element 21, and the outermost negative electrode current collector is disposed on one or both surfaces. A negative electrode active material layer may be disposed.

  The positive electrode current collector 11 and the negative electrode current collector 12 are each provided with a positive electrode current collector plate (tab) 25 and a negative electrode current collector plate (tab) 27 that are electrically connected to the respective electrodes (positive electrode and negative electrode). It has a structure led out of the laminate film 29 so as to be sandwiched between the end portions. The positive electrode current collector plate 25 and the negative electrode current collector plate 27 are ultrasonically welded to the positive electrode current collector 11 and the negative electrode current collector 12 of each electrode, respectively, via a positive electrode lead and a negative electrode lead (not shown) as necessary. Or resistance welding or the like.

  Note that FIG. 2 illustrates a flat battery (stacked battery) that is not a bipolar battery, but a positive electrode active material layer that is electrically coupled to one surface of the current collector and the opposite side of the current collector. And a bipolar battery including a bipolar electrode having a negative electrode active material layer electrically coupled to the surface. In this case, one current collector also serves as a positive electrode current collector and a negative electrode current collector.

  Hereinafter, each member will be described in more detail.

[Negative electrode active material layer]
The negative electrode active material layer includes a negative electrode active material. Examples of the negative electrode active material include carbon materials such as graphite (graphite), soft carbon, and hard carbon, lithium-transition metal composite oxides (for example, Li ₄ Ti ₅ O ₁₂ ), metal materials, lithium alloy negative electrode materials, and the like. Is mentioned. In some cases, two or more negative electrode active materials may be used in combination. Preferably, from the viewpoint of capacity and output characteristics, a carbon material or a lithium-transition metal composite oxide is used as the negative electrode active material. Of course, negative electrode active materials other than those described above may be used.

  The average particle diameter of each active material contained in the negative electrode active material layer is not particularly limited, but is preferably 1 to 100 μm, more preferably 1 to 30 μm from the viewpoint of increasing output.

  When the negative electrode active material layer contains a binder, it is preferable to contain an aqueous binder. In addition to the easy procurement of water as a raw material, water-based binders can be greatly reduced in capital investment on the production line and reduced environmental load because it is water vapor that occurs during drying. There is an advantage.

  The water-based binder refers to a binder using water as a solvent or a dispersion medium, and specifically includes a thermoplastic resin, a polymer having rubber elasticity, a water-soluble polymer, or a mixture thereof. Here, the binder using water as a dispersion medium refers to a polymer that includes all expressed as latex or emulsion and is emulsified or suspended in water. For example, a polymer latex that is emulsion-polymerized in a system that self-emulsifies. Kind.

  Specific examples of water-based binders include styrene polymers (styrene-butadiene rubber, styrene-vinyl acetate copolymer, styrene-acrylic copolymer, etc.), acrylonitrile-butadiene rubber, methyl methacrylate-butadiene rubber, (meta ) Acrylic polymers (polyethyl acrylate, polyethyl methacrylate, polypropyl acrylate, polymethyl methacrylate (methyl methacrylate rubber), polypropyl methacrylate, polyisopropyl acrylate, polyisopropyl methacrylate, polybutyl acrylate, polybutyl methacrylate, polyhexyl acrylate , Polyhexyl methacrylate, polyethylhexyl acrylate, polyethylhexyl methacrylate, polylauryl acrylate, polylauryl methacrylate Relate, etc.), polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene copolymer, polybutadiene, butyl rubber, fluororubber, polyethylene oxide, polyepichlorohydrin, polyphosphazene, polyacrylonitrile, polystyrene, ethylene-propylene-diene copolymer , Polyvinyl pyridine, chlorosulfonated polyethylene, polyester resin, phenol resin, epoxy resin; polyvinyl alcohol (average polymerization degree is preferably 200 to 4000, more preferably 1000 to 3000, and saponification degree is preferably 80. Mol% or more, more preferably 90 mol% or more) and a modified product thereof (saponified product of 1 to 80 mol% of vinyl acetate units of a copolymer of ethylene / vinyl acetate = 2/98 to 30/70 mol ratio) , Poly Nyl alcohol 1-50 mol% partially acetalized product), starch and modified products thereof (oxidized starch, phosphate esterified starch, cationized starch, etc.), cellulose derivatives (carboxymethylcellulose, methylcellulose, hydroxypropylcellulose, hydroxyethylcellulose, And their salts), polyvinylpyrrolidone, polyacrylic acid (salt), polyethylene glycol, (meth) acrylamide and / or (meth) acrylate copolymer [(meth) acrylamide polymer, (meth) acrylamide- (Meth) acrylate copolymer, alkyl (meth) acrylate (1 to 4 carbon atoms) ester- (meth) acrylate copolymer, etc.], styrene-maleate copolymer, polyacrylamide Mannich Denatured body Formalin condensation type resin (urea-formalin resin, melamine-formalin resin, etc.), polyamide polyamine or dialkylamine-epichlorohydrin copolymer, polyethyleneimine, casein, soy protein, synthetic protein, and water-soluble polymers such as mannangalactan derivatives Is mentioned. These aqueous binders may be used alone or in combination of two or more.

  The water-based binder may contain at least one rubber-based binder selected from the group consisting of styrene-butadiene rubber, acrylonitrile-butadiene rubber, methyl methacrylate-butadiene rubber, and methyl methacrylate rubber from the viewpoint of binding properties. preferable. Furthermore, it is preferable that the water-based binder contains a styrene-butadiene rubber because the binding property is good.

  When styrene-butadiene rubber is used as the water-based binder, it is preferable to use the water-soluble polymer in combination from the viewpoint of improving coatability. Water-soluble polymers suitable for use in combination with styrene-butadiene rubber include polyvinyl alcohol and modified products thereof, starch and modified products thereof, cellulose derivatives (carboxymethyl cellulose, methyl cellulose, hydroxyethyl cellulose, and salts thereof), polyvinyl Examples include pyrrolidone, polyacrylic acid (salt), or polyethylene glycol. Among them, it is preferable to combine styrene-butadiene rubber and carboxymethyl cellulose as a binder. The mass ratio of the styrene-butadiene rubber and the water-soluble polymer is not particularly limited, but is preferably styrene-butadiene rubber: water-soluble polymer = 1: 0.3 to 0.7. .

  When a negative electrode active material layer contains a binder, it is preferable that content of an aqueous binder is 80-100 mass% among the binders used for a negative electrode active material layer, and it is preferable that it is 90-100 mass%, 100 It is preferable that it is mass%. Examples of the binder other than the water-based binder include binders used in the following positive electrode active material layer.

  The amount of the binder contained in the negative electrode active material layer is not particularly limited as long as it is an amount capable of binding the active material, but is preferably 0 with respect to 100% by mass of the total amount of the negative electrode active material layer. It is 0.5-15 mass%, More preferably, it is 1-10 mass%, More preferably, it is 2-4 mass%, Most preferably, it is 2.5-3.5 mass%. Since the water-based binder has high binding power, the active material layer can be formed with a small amount of addition as compared with the organic solvent-based binder.

  The negative electrode active material layer further includes a conductive additive, an electrolyte (polymer matrix, ion conductive polymer, electrolytic solution, etc.), and other additives such as a lithium salt for increasing ion conductivity, as necessary.

  The conductive assistant refers to an additive that is blended in order to improve the conductivity of the positive electrode active material layer or the negative electrode active material layer. Examples of the conductive auxiliary agent include carbon materials such as carbon black such as acetylene black, graphite, and carbon fiber. When the active material layer contains a conductive additive, an electronic network inside the active material layer is effectively formed, which can contribute to improvement of the output characteristics of the battery.

  Electrolyte salt (lithium salt) will be contained in a negative electrode active material layer because the electrolyte solution mentioned above osmose | permeates a negative electrode active material layer. Therefore, the specific form of the lithium salt that can be contained in the negative electrode active material layer is the same as the lithium salt that constitutes the electrolyte described above.

  Examples of the ion conductive polymer include polyethylene oxide (PEO) -based and polypropylene oxide (PPO) -based polymers.

  The compounding ratio of the components contained in the negative electrode active material layer and the positive electrode active material layer described later is not particularly limited. The blending ratio can be adjusted by appropriately referring to known knowledge about lithium ion secondary batteries.

The density of the negative electrode active material layer is preferably 1.4 to 1.6 g / cm ³ . If the density of the negative electrode active material layer is 1.6 g / cm ³ or less, the gas generated during charging and discharging of the battery can sufficiently escape from the inside of the power generation element, and the long-term cycle characteristics can be further improved. Further, if the density of the negative electrode active material layer is 1.4 g / cm ³ or more, the active material can be connected and the electron conductivity can be sufficiently maintained. As a result, the battery performance can be further improved. The density of the negative electrode active material layer is preferably 1.42 to 1.53 g / cm ³ . Note that the density of the negative electrode active material layer represents the mass of the active material layer per unit volume. Specifically, after removing the negative electrode active material layer from the battery, removing the solvent and the like present in the electrolyte solution, the electrode volume is obtained from the long side, the short side, and the height, and after measuring the weight of the active material layer, It can be determined by dividing weight by volume.

  Moreover, it is preferable that the surface centerline average roughness (Ra) of the separator side surface of a negative electrode active material layer is 0.5-1.0 micrometer. If the center line average roughness (Ra) of the negative electrode active material layer is 0.5 μm or more, the long-term cycle characteristics can be further improved. This is considered to be because if the surface roughness is 0.5 μm or more, the gas generated in the power generation element is easily discharged out of the system. Moreover, if the centerline average roughness (Ra) of the negative electrode active material layer is 1.0 μm or less, the electron conductivity in the battery element is sufficiently secured, and the battery characteristics can be further improved.

  Here, the centerline average roughness Ra means that only the reference length is extracted from the roughness curve in the direction of the average line, the x axis is in the direction of the average line of the extracted portion, and the y axis is in the direction of the vertical magnification. When the roughness curve is expressed by y = f (x), the value obtained by the following formula 1 is expressed in micrometers (μm) (JIS-B0601-1994).

  The value of Ra is measured using a stylus type or non-contact type surface roughness meter that is generally widely used, for example, by a method defined in JIS-B0601-1994. There are no restrictions on the manufacturer or model of the device. In the examination in the present invention, Ra was obtained using a roughness analyzer (manufactured by SLOAN, model number: Dektak3030) based on the method defined in JIS-B0601. Either the contact method (stylus type using a diamond needle or the like) or the non-contact method (non-contact detection using a laser beam or the like) can be used, but in the study in the present invention, the measurement was performed by the contact method.

  Moreover, since it can measure comparatively easily, surface roughness Ra prescribed | regulated to this invention is measured in the step in which the active material layer was formed on the electrical power collector in the manufacture process. However, the measurement can be performed even after the battery is completed, and the results are almost the same as those in the manufacturing stage. Therefore, the surface roughness after the battery is completed may satisfy the above Ra range. The surface roughness of the negative electrode active material layer is that on the separator side of the negative electrode active material layer.

  The surface roughness of the negative electrode takes into account the active material shape, particle diameter, active material blending amount, etc. contained in the negative electrode active material layer, for example, by adjusting the press pressure during active material layer formation, etc. It can adjust so that it may become the said range. The shape of the active material varies depending on the type and manufacturing method, and the shape can be controlled by pulverization, for example, spherical (powder), plate, needle, column, square Etc. Therefore, in order to adjust the surface roughness in consideration of the shape used for the active material layer, active materials having various shapes may be combined.

[Positive electrode active material layer]
The positive electrode active material layer contains a positive electrode active material and, if necessary, other materials such as a conductive additive, a binder, an electrolyte (polymer matrix, ion conductive polymer, electrolyte, etc.), a lithium salt for increasing ion conductivity, and the like. Further includes an additive.

Examples of the positive electrode active material include LiMn ₂ O ₄ , LiCoO ₂ , LiNiO ₂ , Li (Ni—Mn—Co) O _2, and lithium-such as those obtained by replacing some of these transition metals with other elements. Examples include transition metal composite oxides, lithium-transition metal phosphate compounds, and lithium-transition metal sulfate compounds. In some cases, two or more positive electrode active materials may be used in combination. Preferably, a lithium-transition metal composite oxide is used as the positive electrode active material from the viewpoint of capacity and output characteristics. More preferably, Li (Ni—Mn—Co) O ₂ and those in which some of these transition metals are substituted with other elements (hereinafter, also simply referred to as “NMC composite oxide”) are used. The NMC composite oxide has a layered crystal structure in which a lithium atomic layer and a transition metal (Mn, Ni, and Co are arranged in order) are stacked alternately via an oxygen atomic layer. One Li atom is contained, and the amount of Li that can be taken out is twice that of the spinel lithium manganese oxide, that is, the supply capacity is doubled, so that a high capacity can be obtained.

  As described above, the NMC composite oxide includes a composite oxide in which a part of the transition metal element is substituted with another metal element. Other elements in that case include Ti, Zr, Nb, W, P, Al, Mg, V, Ca, Sr, Cr, Fe, B, Ga, In, Si, Mo, Y, Sn, V, Cu , Ag, Zn, etc., preferably Ti, Zr, Nb, W, P, Al, Mg, V, Ca, Sr, Cr, more preferably Ti, Zr, P, Al, Mg, From the viewpoint of improving cycle characteristics, Ti, Zr, Al, Mg, and Cr are more preferable.

Since the NMC composite oxide has a high theoretical discharge capacity, it is preferable that the general formula (1): Li _a Ni _b Mn _c Co _d M _x O ₂ (where a, b, c, d, x Satisfies 0.9 ≦ a ≦ 1.2, 0 <b <1, 0 <c ≦ 0.5, 0 <d ≦ 0.5, 0 ≦ x ≦ 0.3, and b + c + d = 1. And at least one element selected from Ti, Zr, Nb, W, P, Al, Mg, V, Ca, Sr, and Cr. Here, a represents the atomic ratio of Li, b represents the atomic ratio of Ni, c represents the atomic ratio of Mn, d represents the atomic ratio of Co, and x represents the atomic ratio of M. Represents. From the viewpoint of cycle characteristics, it is preferable that 0.4 ≦ b ≦ 0.6 in the general formula (1). The composition of each element can be measured by, for example, inductively coupled plasma (ICP) emission spectrometry.

  In general, nickel (Ni), cobalt (Co), and manganese (Mn) are known to contribute to capacity and output characteristics from the viewpoint of improving the purity of materials and improving electronic conductivity. Ti or the like partially replaces the transition metal in the crystal lattice. From the viewpoint of cycle characteristics, it is preferable that a part of the transition element is substituted with another metal element, and it is particularly preferable that 0 <x ≦ 0.3 in the general formula (1). Since at least one selected from the group consisting of Ti, Zr, Nb, W, P, Al, Mg, V, Ca, Sr, and Cr is dissolved, the crystal structure is stabilized. It is considered that the battery capacity can be prevented from decreasing even if the above is repeated, and that excellent cycle characteristics can be realized.

  As a more preferable embodiment, in the general formula (1), b, c and d are 0.44 ≦ b ≦ 0.51, 0.27 ≦ c ≦ 0.31, 0.19 ≦ d ≦ 0.26. It is preferable that it is excellent in balance between capacity and durability.

  Of course, positive electrode active materials other than those described above may be used.

  The average particle size of the active material contained in the positive electrode active material layer is not particularly limited, but is preferably 1 to 100 μm, more preferably 1 to 20 μm from the viewpoint of increasing the output.

  Although it does not specifically limit as a binder used for a positive electrode active material layer, For example, the following materials are mentioned. Polyethylene, polypropylene, polyethylene terephthalate (PET), polyether nitrile, polyacrylonitrile, polyimide, polyamide, cellulose, carboxymethyl cellulose (CMC) and its salts, ethylene-vinyl acetate copolymer, polyvinyl chloride, styrene-butadiene rubber (SBR) ), Isoprene rubber, butadiene rubber, ethylene / propylene rubber, ethylene / propylene / diene copolymer, styrene / butadiene / styrene block copolymer and hydrogenated product thereof, styrene / isoprene / styrene block copolymer and hydrogenated product thereof Thermoplastic polymers such as products, polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer (F P), tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer (PFA), ethylene / tetrafluoroethylene copolymer (ETFE), polychlorotrifluoroethylene (PCTFE), ethylene / chlorotrifluoroethylene copolymer (ECTFE) ), Fluororesin such as polyvinyl fluoride (PVF), vinylidene fluoride-hexafluoropropylene-based fluororubber (VDF-HFP-based fluororubber), vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene-based fluororubber (VDF-HFP) -TFE fluorine rubber), vinylidene fluoride-pentafluoropropylene fluorine rubber (VDF-PFP fluorine rubber), vinylidene fluoride-pentafluoropropylene-tetrafluoroethylene Fluorine rubber (VDF-PFP-TFE fluorine rubber), vinylidene fluoride-perfluoromethyl vinyl ether-tetrafluoroethylene fluorine rubber (VDF-PFMVE-TFE fluorine rubber), vinylidene fluoride-chlorotrifluoroethylene fluorine Examples thereof include vinylidene fluoride fluorine rubber such as rubber (VDF-CTFE fluorine rubber), epoxy resin, and the like. These binders may be used independently and may use 2 or more types together.

  The amount of the binder contained in the positive electrode active material layer is not particularly limited as long as it is an amount capable of binding the active material, but is preferably 0.5 to 15% by mass with respect to the active material layer. More preferably, it is 1-10 mass%.

  About other additives other than a binder, the thing similar to the column of the said negative electrode active material layer can be used.

[Separator (electrolyte layer)]
The separator has a function of holding an electrolyte and ensuring lithium ion conductivity between the positive electrode and the negative electrode, and a function as a partition wall between the positive electrode and the negative electrode.

  Here, in order to further improve the release of the gas generated during the initial charge of the battery from the power generation element, it is preferable to consider the release of the gas that has passed through the negative electrode active material layer and reached the separator. From such a viewpoint, it is more preferable that the air permeability and the porosity of the separator are within an appropriate range.

  Specifically, the air permeability (Gurley value) of the separator is preferably 200 (seconds / 100 cc) or less. When the separator has an air permeability of 200 (seconds / 100 cc) or less, the escape of gas generated is improved, the battery has a good capacity retention rate after cycling, and the short circuit prevention and machine functions as a separator The physical properties are also sufficient. The lower limit of the air permeability is not particularly limited, but is usually 300 (second / 100 cc) or more. The air permeability of the separator is a value according to the measurement method of JIS P8117 (2009).

Moreover, it is preferable that the porosity of a separator is 40 to 65%. When the separator has a porosity of 40 to 65%, the release of generated gas is improved, the battery has better long-term cycle characteristics, and the short circuit prevention and mechanical properties that are functions as a separator are also provided. It will be enough. For the porosity, a value obtained as a volume ratio from the density of the resin as the raw material of the separator and the density of the separator of the final product is adopted. For example, when the density of the raw material resin is ρ and the bulk density of the separator is ρ ′, the porosity is expressed by 100 × (1−ρ ′ / ρ).

Examples of the separator include a porous sheet separator or a nonwoven fabric separator made of a polymer or fiber that absorbs and holds the electrolyte.

  As a separator for a porous sheet made of a polymer or fiber, for example, a microporous (microporous film) can be used. Specific examples of the porous sheet made of the polymer or fiber include polyolefins such as polyethylene (PE) and polypropylene (PP); a laminate in which a plurality of these are laminated (for example, three layers of PP / PE / PP) And a microporous (microporous membrane) separator made of a hydrocarbon resin such as polyimide, aramid, polyvinylidene fluoride-hexafluoropropylene (PVdF-HFP), glass fiber, and the like.

  The thickness of the microporous (microporous membrane) separator cannot be uniquely defined because it varies depending on the intended use. For example, in applications such as secondary batteries for driving motors such as electric vehicles (EV), hybrid electric vehicles (HEV), and fuel cell vehicles (FCV), it is 4 to 60 μm in a single layer or multiple layers. Is desirable. The fine pore diameter of the microporous (microporous membrane) separator is desirably 1 μm or less (usually a pore diameter of about several tens of nm).

  As the nonwoven fabric separator, cotton, rayon, acetate, nylon, polyester; polyolefins such as PP and PE; conventionally known ones such as polyimide and aramid are used alone or in combination. The bulk density of the nonwoven fabric is not particularly limited as long as sufficient battery characteristics can be obtained by the impregnated polymer gel electrolyte.

  The nonwoven fabric separator preferably has a porosity of 50 to 90%. Furthermore, the thickness of the nonwoven fabric separator may be the same as that of the electrolyte layer, preferably 5 to 200 μm, particularly preferably 10 to 100 μm.

  Here, the separator may be a separator in which a heat-resistant insulating layer is laminated on at least one surface of the resin porous substrate. The heat-resistant insulating layer is a ceramic layer containing inorganic particles and a binder. By having the heat-resistant insulating layer, the internal stress of the separator that increases when the temperature rises is relieved, so that the effect of suppressing thermal shrinkage can be obtained. Moreover, by having a heat-resistant insulating layer, the mechanical strength of the separator with a heat-resistant insulating layer is improved, and it is difficult for the separator to break. Furthermore, the separator is less likely to curl in the electrical device manufacturing process due to the effect of suppressing thermal shrinkage and high mechanical strength. Further, the ceramic layer is preferable because it can also function as a gas releasing means for improving the gas releasing property from the power generation element.

  Moreover, in this embodiment, a separator hold | maintains electrolyte solution. A liquid electrolyte or a gel polymer electrolyte is used as the electrolytic solution. These electrolytic solutions have a function as a lithium ion carrier.

The liquid electrolyte has a form in which a lithium salt is dissolved in an organic solvent. Examples of the organic solvent used include carbonates such as ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate. As the lithium _{salt, Li (CF 3 SO 2)} 2 N, Li (C 2 F 5 SO 2) 2 N, LiPF 6, LiBF 4, LiClO 4, LiAsF 6, LiTaF such 6, LiCF ₃ SO ₃ A compound that can be added to the active material layer of the electrode can be similarly employed.

  Moreover, in this embodiment, electrolyte solution contains an electrode protective agent. The “electrode protective agent” is an agent having a function of protecting the electrode (preventing electrode deterioration), and a conventionally known compound can be suitably used. Preferably, the electrode protecting agent has a function of preventing the deterioration of the negative electrode active material by forming an SEI film on the surface of the negative electrode active material. Specific examples of the electrode protecting agent include, for example, vinylene carbonate, vinyl ethylene carbonate, fluoroethylene carbonate, difluoroethylene carbonate, methyl vinylene carbonate, dimethyl vinylene carbonate, phenyl vinylene carbonate, diphenyl vinylene carbonate, ethyl vinylene carbonate, diethyl vinylene carbonate, 1,2-divinylethylene carbonate, 1-methyl-1-vinylethylene carbonate, 1-methyl-2-vinylethylene carbonate, 1-ethyl-1-vinylethylene carbonate, 1-ethyl-2-vinylethylene carbonate, vinylvinylene Carbonate, allylethylene carbonate, vinyloxymethylethylene carbonate, allyloxymethylethylene car Acrylate, acryloxymethyl ethylene carbonate, methacryloxymethyl ethylene carbonate, ethynyl ethylene carbonate, propargyl ethylene carbonate, ethynyloxymethyl ethylene carbonate, propargyl oxyethylene carbonate, methylene ethylene carbonate, 1,1-dimethyl-2-methylene ethylene carbonate, etc. Can be mentioned. Among these, vinylene carbonate, vinyl ethylene carbonate, fluoroethylene carbonate, and difluoroethylene carbonate are preferable as those having particularly excellent electrode protecting action and contributing to improvement in cycle durability, and vinylene carbonate and fluoroethylene carbonate are more preferable. preferable. As for these electrode protective agents, only 1 type may be used independently and 2 or more types may be used together.

  Moreover, cyclic sulfonic acid ester is mentioned as another preferable form of an electrode protective agent. By including a cyclic sulfonic acid ester as an electrode protective agent, higher life performance can be obtained. As the cyclic sulfonate ester, the following formula (1):

Where
O represents oxygen and S represents sulfur;
A, B and D each independently represent at least one group selected from the group consisting of a single bond, oxygen, sulfur, carbonyl group, thiocarbonyl group, sulfinyl group, sulfonyl group, and NR ⁵ group; In this case, R ⁵ represents at least one group selected from the group consisting of a hydrogen atom, a monovalent aliphatic hydrocarbon group, a monovalent alicyclic hydrocarbon group, and a monovalent aromatic hydrocarbon group. ,
R ¹ , R ² , R ³ and R ⁴ each independently represents a single bond or a divalent aliphatic hydrocarbon group,
It is preferable that it is a compound represented by these.

In the formula (1), R ⁵ is at least one selected from the group consisting of a hydrogen atom, a monovalent aliphatic hydrocarbon group, a monovalent alicyclic hydrocarbon group, and a monovalent aromatic hydrocarbon group. It is a group. The aliphatic hydrocarbon group is preferably a linear or branched alkyl group having 1 to 10 carbon atoms, more preferably 1 to 5 carbon atoms, and still more preferably 1 to 3 carbon atoms. Group, n-propyl group, n-butyl group, n-pentyl group (amyl group), n-hexyl group, n-heptyl group, n-octyl group, n-nonyl group, n-decyl group, i-propyl group , Sec-butyl group, i-butyl group, t-butyl group, 1-methylbutyl group, 1-ethylpropyl group, 2-methylbutyl group, neopentyl group, 1,2-dimethylpropyl group, 1,1-dimethylpropyl group 1,3-dimethylbutyl group, 3,3-dimethylbutyl group, 2-ethylbutyl group, 2-ethyl-2-methylpropyl group, 1-methylheptyl group, 2-ethylhexyl group, 1,5-dimethyl group Hexyl group, t- octyl group. The alicyclic hydrocarbon group is preferably a cycloalkyl group having 1 to 10 carbon atoms, more preferably 1 to 5 carbon atoms, and still more preferably 1 to 3 carbon atoms. For example, cyclopropyl group, cyclopropylmethyl Group, cyclobutyl group, cyclobutylmethyl group, cyclopentyl group, cyclohexyl group, cyclohexylmethyl group, cycloheptyl group, cyclooctyl group, cyclohexylpropyl group, cyclododecyl group, norbornyl group (C7), adamantyl group (C10), cyclopentylethyl Group and the like. The aromatic hydrocarbon group is preferably an aryl group having 1 to 10 carbon atoms, more preferably 1 to 5 carbon atoms, and still more preferably 1 to 3 carbon atoms. For example, a phenyl group, an alkylphenyl group, an alkylphenyl group. And phenyl group and naphthyl group substituted with a group.

R ¹ , R ² , R ³ and R ⁴ each independently represents a single bond or a divalent aliphatic hydrocarbon group. The divalent aliphatic hydrocarbon group is preferably a linear or branched alkylene group having preferably 1 to 10 carbon atoms, more preferably 1 to 5 carbon atoms, and still more preferably 1 to 3 carbon atoms. , Methylene group, ethylene group, trimethylene group, isopropylene group, tetramethylene group and the like.

  Further, the cyclic sulfonate ester has the following formula (2):

Where
Z is an alkylene group having 1 to 5 carbon atoms or a sulfonylalkylene group,
It is more preferable that it is a compound represented by these. The cyclic sulfonic acid ester represented by the formula (2) also includes a disulfonic acid compound in which Z is a sulfonylalkylene group (—SO ₂ —C _n H _2n —). As a disulfonic acid compound, as an alkylene group, C1-C3 is more preferable.

  Examples of the cyclic sulfonic acid ester represented by the formula (1) or the formula (2) include 1,3-propane sultone, 1,4-butane sultone, 2,4-butane sultone, and the like, but are not limited thereto. It is not a thing. That is, as the cyclic sulfonic acid ester represented by the formula (1) or the formula (2), a cyclic disulfonic acid ester having two sulfonyl groups is also preferably used.

  The gel polymer electrolyte has a configuration in which the liquid electrolyte is injected into a matrix polymer (host polymer) made of an ion conductive polymer. By using a gel polymer electrolyte as the electrolytic solution, the fluidity of the electrolyte is lost, and it is excellent in that it is easy to block the ion conductivity between the respective layers. Examples of the ion conductive polymer used as the matrix polymer (host polymer) include polyethylene oxide (PEO), polypropylene oxide (PPO), and copolymers thereof. In such polyalkylene oxide polymers, electrolyte salts such as lithium salts can be well dissolved.

  The matrix polymer of gel electrolyte can express excellent mechanical strength by forming a crosslinked structure. In order to form a crosslinked structure, thermal polymerization, ultraviolet polymerization, radiation polymerization, electron beam polymerization, etc. are performed on a polymerizable polymer (for example, PEO or PPO) for forming a polymer electrolyte using an appropriate polymerization initiator. A polymerization treatment may be performed.

[Current collector]
There is no particular limitation on the material constituting the current collector, but a metal is preferably used.

  Specifically, examples of the metal include aluminum, nickel, iron, stainless steel, titanium, copper, and other alloys. In addition to these, a clad material of nickel and aluminum, a clad material of copper and aluminum, or a plating material of a combination of these metals can be preferably used. Moreover, the foil by which aluminum is coat | covered on the metal surface may be sufficient. Of these, aluminum, stainless steel, and copper are preferable from the viewpoints of electronic conductivity and battery operating potential.

  The size of the current collector is determined according to the intended use of the battery. For example, if it is used for a large battery that requires a high energy density, a current collector having a large area is used. There is no particular limitation on the thickness of the current collector. The thickness of the current collector is usually about 1 to 100 μm.

[Positive electrode current collector and negative electrode current collector]
The material which comprises a current collector plate (25, 27) is not restrict | limited in particular, The well-known highly electroconductive material conventionally used as a current collector plate for lithium ion secondary batteries can be used. As a constituent material of the current collector plate, for example, metal materials such as aluminum, copper, titanium, nickel, stainless steel (SUS), and alloys thereof are preferable. From the viewpoint of light weight, corrosion resistance, and high conductivity, aluminum and copper are more preferable, and aluminum is particularly preferable. In addition, the same material may be used for the positive electrode current collecting plate 27 and the negative electrode current collecting plate 25, and different materials may be used.

[Positive lead and negative lead]
Moreover, although illustration is abbreviate | omitted, you may electrically connect between the collector 11 and the current collector plates (25, 27) via a positive electrode lead or a negative electrode lead. As a constituent material of the positive electrode and the negative electrode lead, materials used in known lithium ion secondary batteries can be similarly employed. In addition, heat-shrinkable heat-shrinkable parts are removed from the exterior so that they do not affect products (for example, automobile parts, especially electronic devices) by touching peripheral devices or wiring and causing leakage. It is preferable to coat with a tube or the like.

[Exterior body]
The exterior body is a member that encloses the power generation element therein, and a bag-like case using a laminate film containing aluminum that can cover the power generation element can be used. As the laminate film, for example, a laminate film having a three-layer structure in which PP, aluminum, and nylon are laminated in this order can be used, but is not limited thereto. A laminate film is desirable from the viewpoint that it is excellent in high output and cooling performance, and can be suitably used for a battery for large equipment for EV and HEV. Moreover, since the group pressure to the electric power generation element applied from the outside can be adjusted easily, the exterior body is more preferably a laminate film containing aluminum.

  In the present embodiment, the inner volume of the laminate film 29 which is an exterior body is configured to be larger than the volume of the power generation element 21 so that the power generation element 21 can be enclosed. In other words, in the present embodiment, the power generation element 21 has an excess space (reference numeral 30 shown in FIG. 2) inside the laminate film 29 that is an exterior body together with the above-described electrolyte (including the electrode protective agent). Is enclosed. Here, the internal volume of the exterior body refers to the volume in the exterior body before vacuuming after sealing with the exterior body. The volume of the power generation element is the volume of the space occupied by the power generation element, and includes a hole in the power generation element. When the external pressure applied to the secondary battery 10 by the pressurizing device 4 decreases due to the inner volume of the exterior body being larger than the volume of the power generation element, the electrode protective agent contained in the electrolyte solution is contained inside the power generation element 21. It moves to (between electrodes) and tends to exhibit the function of protecting the electrodes. Conversely, when the external pressure applied to the secondary battery 10 by the pressurizer 4 increases, the electrode protective agent moves from the inside of the power generation element 21 (between the electrodes) to the surplus space 30 to protect the electrodes. There is a tendency that the function is not exhibited.

  In automobile applications and the like, recently, a large-sized battery is required. The effect of the present invention of improving the cycle durability of several hundred cycles by effectively functioning the electrode protective agent is effective in the case of a large area battery with a large amount of coating (SEI) formed on the surface of the negative electrode active material. Can be expressed more effectively. Therefore, in this invention, it is preferable in the meaning that the effect of this invention is exhibited more that a battery structure is large sized. Specifically, the negative electrode active material layer is preferably rectangular, and the length of the short side of the rectangle is preferably 100 mm or more. Such a large battery can be used for vehicle applications. Here, the length of the short side of the negative electrode active material layer refers to the side having the shortest length among the electrodes. The upper limit of the length of the short side of the battery structure is not particularly limited, but is usually 250 mm or less.

Further, as a viewpoint of a large-sized battery, which is different from the viewpoint of the physical size of the electrode, it is possible to regulate the size of the battery from the relationship between the battery area and the battery capacity. For example, in the case of a flat laminated battery, the value of the ratio of the battery area to the rated capacity (the maximum value of the projected area of the battery including the battery outer casing) is 5 cm ² / Ah or more, and the rated capacity is In a battery having a capacity of 3 Ah or more, a decrease in discharge capacity tends to become apparent when charging / discharging of several hundred cycles is repeated. Therefore, it is preferable that the lithium ion secondary battery according to the present embodiment is a battery having a large size as described above, from the viewpoint that the merit due to the manifestation of the effects of the present invention is greater. Furthermore, the aspect ratio of the rectangular electrode is preferably 1 to 3, and more preferably 1 to 2. The electrode aspect ratio is defined as the aspect ratio of the rectangular positive electrode active material layer. By setting the aspect ratio in such a range, it is possible to uniformly discharge the gas generated during charging / discharging in the surface direction and to prevent various problems caused by the generation of the gas. .

  Referring to FIG. 1 again, the secondary battery 10 is connected to a load 50, and an inverter 51 for converting the current supplied to the load 50 from direct current to alternating current is interposed in the circuit. On the circuit from the secondary battery 10 to the load 50, an ammeter 31 is connected in series, and a voltmeter 32 is connected in parallel. The ammeter 31 and the voltmeter 32 are connected to the controller 3, and each measured value is input to the controller 3. A relay switch 33 that opens and closes in response to a command from the controller 3 is provided at an output terminal from the secondary battery 10. This relay switch 33 opens and closes the circuit in order to measure the open circuit voltage and the closed circuit voltage of the secondary battery 10. The open circuit voltage is a voltage when the load 50 is not connected (also referred to as an open voltage), and the closed circuit voltage is a voltage when the load 50 is connected. In addition, an external pressure sensor 34 is disposed outside (lower) the secondary battery 10. The external pressure sensor 34 is a device (external pressure detecting means) that detects the external pressure P applied to the secondary battery 10 by the pressurizing device 4. This external pressure sensor 34 is also connected to the controller 3 and outputs a signal of the detected external pressure P to the controller 3. In addition, as the external pressure sensor 34, for example, a film type pressure distribution measuring system manufactured by tekscan can be used, but the invention is not limited thereto. As described above, it is possible to apply a more appropriate external pressure to the secondary battery 10 by detecting the external pressure using the external pressure sensor 34 and performing control by the control unit based on the detected value. . However, the use of external pressure detection means such as the external pressure sensor 34 is not essential.

  Furthermore, an auxiliary power source 35 is provided in this circuit. The auxiliary power source 35 may be, for example, a secondary battery (storage battery) or a primary battery when the entire circuit is operating alone. When this circuit is connected to an external power source, for example, when connected to an external power source to charge the secondary battery 10, the external power source becomes the auxiliary power source 35.

  The auxiliary power source 35 is a power source for operating the controller 3 and the pressurizing device 4 when the remaining capacity of the secondary battery 10 decreases. When the remaining capacity of the secondary battery 10 is more than the amount necessary for operating the controller 3 and the pressurizing device 4 at normal times, the power source for the secondary battery 10 to operate the controller 3 and the pressurizing device 4 is used. It becomes.

  On the other hand, as shown in FIGS. 3 and 4, the pressure device 4 includes a movable regulating plate 41 between the lower plate 42 and the upper plate 43. The lower plate 42 and the regulation plate 41 sandwich the secondary battery 10 and apply an external pressure P to the secondary battery 10. The lower plate 42 and the upper plate 43 are connected and fixed by bolts and nuts 44. On the other hand, ball screws 45 are provided at the four corners of the restriction plate 41. 3 and 4, illustration of the positive electrode current collector plate 25 and the negative electrode current collector plate 27 (see FIG. 2) of the secondary battery 10 is omitted.

  A screw shaft 46 of the ball screw 45 is rotatably attached to the lower plate 42 and the upper plate 43. A part of the screw shaft 46 protrudes from the upper plate 43. A gear (not shown) is engaged with the protruding portion and connected to the motor 48. On the other hand, the nut portion 47 of the ball screw 45 is fixed to the restriction plate 41. The position of the restricting plate 41 is moved between the upper plate 43 and the lower plate 42 when the screw shafts 46 of the four ball screws 45 are rotated by the motor 48. Thereby, the external pressure P applied to the secondary battery 10 changes.

  Here, it is preferable to use a servo motor with an encoder, a stepping motor or the like so that the motor 48 operates in synchronization with the four ball screws 45. The controller 3 grasps the position of the restricting plate 41 based on a signal from the encoder and synchronizes the four ball screws 45 so that the restricting plate 41 is moved without being tilted. Then, the position of the restriction plate 41 provided in this way moves according to a command from the controller 3, so that the interval between the lower plate 42 and the restriction plate 41 changes and the external pressure P is indirectly adjusted.

  Note that the mechanism of the pressurizing device 4 (here, a mechanical mechanism such as a bolt nut 44 for fixing the upper plate 43 and the lower plate 42, a ball screw 45, a motor 48, a gear) is limited to the configuration described above. Is not to be done. Such a mechanism may have any configuration as long as the external pressure P applied to the secondary battery 10 can be controlled (adjusted). For example, instead of the ball screw 45, a simple feed screw may be adopted. In addition to the screw mechanism such as the ball screw 45 and the feed screw, the restriction plate 41 may be moved using a pneumatic cylinder or a hydraulic cylinder. Further, the bolt nut 44 for fixing the upper plate 43 and the lower plate 42 may be replaced with the upper plate 43 and the lower plate 42 by the side wall surface, or the restriction plate 41 movable inside may be provided. It can also be set as the can body structure provided. Furthermore, the secondary battery is placed inside a module can made of stainless steel or the like, and the internal pressure of the can is adjusted using a pressurizing device connected to the module can. A pressurizing unit that applies pressure may be employed.

  The controller 3 controls the position of the regulation plate 41 from at least one of the remaining capacity, open circuit voltage, and closed circuit voltage of the secondary battery 10 obtained from the input current value, voltage value, and time. It also functions as an SOC calculation means for calculating the SOC. Such a controller 3 can be composed of, for example, a CPU (Central Processing Unit).

  Next, control of the secondary battery system configured as described above will be described.

  The basic control of the secondary battery system in the present embodiment is to adjust the external pressure P applied by the pressurizing device 4 according to the SOC of the secondary battery 10 during charging and discharging.

  “SOC (State Of Charge)” refers to the ratio of the capacity in a fully charged state to the capacity at the current time point. There are various methods for calculating (estimating) this SOC. For example, there are a method of estimating from the open circuit voltage and the internal resistance of the battery, a method of time integrating the current value, and the like. In order to be able to obtain the SOC even when the load 50 is connected to the secondary battery system, it is necessary to employ a method of integrating the current value over time. Specifically, an amount of current (current × time) that can be taken out from a full charge is obtained in advance, and from that, the sum of the value of discharge and charge and the discharge time is subtracted (or added). ), The remaining capacity can be easily obtained. That is, battery remaining capacity (SOC) = initial capacity ± current value × time. Here, the sign of ± is + at the time of charging and − at the time of discharging. In addition, about SOC, it is preferable to correct | amend every time full charge is performed so that the time of full charge may be 100%. The calculation (estimation) of the SOC is not limited to such a method, and other methods may be used.

  Next, the control procedure of the secondary battery system according to the present embodiment will be described with reference to the flowchart showing the control procedure of the secondary battery system shown in FIG.

  First, in step S101, the controller 3 calculates the SOC of the secondary battery 10.

  Subsequently, based on the calculated SOC of the secondary battery 10, the controller 3 controls the distance between the lower plate 42 and the regulation plate 41 of the pressure device 4 as necessary, so that the pressure device 4 applies The external pressure P to be adjusted is adjusted. This point will be described in detail below.

  In step S102, the controller 3 determines whether or not the calculated SOC of the secondary battery 10 is equal to or greater than a predetermined value (SOC1). The predetermined value (SOC1) can be appropriately set according to the type of the structure and material of the secondary battery, and is 3 to 5%, for example. The inventors of the present invention have found that when the threshold value of the SOC is extremely small, the deterioration of the electrode is likely to proceed. When this condition is satisfied (that is, SOC ≧ SOC1) (for example, when the battery is discharged from the fully charged state and the discharge capacity remains to some extent), it is determined YES in this step, and the step The process proceeds to S103. On the other hand, when this condition is not satisfied (that is, SOC <SOC1) (for example, when the SOC gradually decreases and falls below SOC1 during discharge), NO is determined in this step, and step The process proceeds to S104.

If YES is determined in step S102, in step S103, the controller 3 determines whether or not the external pressure P detected by the external pressure sensor 34 is a value within a predetermined range (first predetermined range). Judging. Here, the first predetermined range is a relatively large external pressure range suitable for the case of SOC ≧ SOC1, and the pressure in the stacking direction of the power generation elements of the secondary battery 10 is preferably 0.4 to. It can be set to 1.5 kgf / cm ² . In step S103, when this condition is satisfied (that is, the external pressure P is a value within the first predetermined range), YES is determined in this step, and the process returns to step S101. On the other hand, if this condition is not satisfied (that is, the external pressure P is outside the first predetermined range), NO is determined in this step, and the process proceeds to step S105.

  If NO is determined in step S103, in step S105, the controller 3 controls the pressure device 4 to adjust the external pressure P applied by the pressure device 4. Specifically, the external pressure P is adjusted to be a value within the first predetermined range by controlling the distance between the lower plate 42 and the regulating plate 41 of the pressurizing device 4. When the adjustment of the external pressure P is completed in step S105, the process proceeds to step S106.

On the other hand, if NO is determined in step S102, in step S104, the controller 3 determines whether or not the external pressure P detected by the external pressure sensor 34 is a value within a predetermined range (second predetermined range). Judge whether or not. Here, the second predetermined range is a range of a relatively small external pressure suitable when SOC <SOC1, and the pressure in the stacking direction of the power generation elements of the secondary battery 10 is preferably 0.1 kgf / It can be set to cm ² or more and less than 0.4 kgf / cm ² . In step S104, if this condition is satisfied (that is, the external pressure P is a value within the second predetermined range), YES is determined in this step, and the process returns to step S101. On the other hand, if this condition is not satisfied (that is, the external pressure P is outside the second predetermined range), NO is determined in this step, and the process proceeds to step S105.

  If NO is determined in step S104, in step S105, the controller 3 controls the pressurizing device 4 to adjust the external pressure P applied by the pressurizing device 4. Specifically, the external pressure P is adjusted to a value within the second predetermined range by controlling the distance between the lower plate 42 and the regulating plate 41 of the pressurizing device 4. When the adjustment of the external pressure P is completed in step S105, the process proceeds to step S106.

  In step S106, the controller 3 determines whether charging / discharging of the secondary battery 10 is completed (whether the secondary battery 10 is in a charged state or a discharged state). When this condition is satisfied (that is, the secondary battery 10 is neither in a charged state nor a discharged state), the control of the secondary battery system according to the present embodiment is finished. On the other hand, when this condition is not satisfied (that is, the secondary battery 10 is in a charged state or a discharged state), the control returns to step S101 in order to continue control of the secondary battery system according to the present embodiment. In addition, it can be determined by arbitrary methods whether charging / discharging of the secondary battery 10 was complete | finished. For example, at the time of discharging, it can be determined that the discharging has ended when the measured value of the current input from the ammeter 31 to the controller 3 becomes zero. However, it is not necessarily limited to such a form.

As described above, according to the study by the present inventors, the cause of the decrease in the cycle durability in the so-called laminate battery is the deterioration of the active material layer in a region where the SOC of the battery is as small as several percent (low SOC region). It was found. Based on this knowledge, in the nonaqueous electrolyte secondary battery system according to the present embodiment, when the SOC of the secondary battery 10 is equal to or higher than a predetermined value (SOC ≧ SOC1), the external pressure P is in a relatively large range ( For example, it is adjusted to 0.4 to 1.5 kgf / cm ² ). Thereby, the electrode protective agent contained in the electrolytic solution tends to move from the inside of the power generation element 21 (between the electrodes) to the surplus space 30 and the function of protecting the electrodes is not exhibited. As a result, when SOC ≧ SOC1 (the active material layer does not deteriorate so much, the function of the electrode protective agent does not need to be exhibited), wasteful consumption of the electrode protective agent is suppressed, and the electrode protective agent is effective. Can be used.

On the other hand, in the nonaqueous electrolyte secondary battery system according to the present embodiment, when the SOC of the secondary battery 10 is less than a predetermined value (SOC <SOC1), the external pressure P is in a relatively small range (for example, 0 0.1 kgf / cm ² or more and 0.4 kgf / cm ² ). Thereby, the electrode protecting agent contained in the electrolytic solution tends to move to the inside of the power generation element 21 (between the electrodes), and the function of protecting the electrodes tends to be exhibited. As a result, when SOC <SOC1 (deterioration of the active material layer can proceed, the function of the electrode protection agent needs to be exhibited), the degradation of the active material layer is suppressed by the action of the electrode protection agent. The As a result, a decrease in cycle durability in the laminate battery is suppressed, and it is possible to improve the cycle durability of several hundred cycles required when used as a power source for an electric vehicle.

  Hereinafter, a result (Example) of actually producing a lithium ion secondary battery and performing a charge / discharge cycle test while adjusting the external pressure applied to the lithium ion secondary battery using the secondary battery system according to the present invention will be described. .

[1. Preparation of electrolyte]
A mixed solvent (30:30:40 (volume ratio)) of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) was used as a solvent. Further, 1.0M LiPF ₆ was used as a lithium salt. Note that “1.0 M LiPF ₆ ” means that the lithium salt (LiPF ₆ ) concentration in the mixture of the mixed solvent and the lithium salt is 1.0 M.

[2. Preparation of positive electrode]
A solid content comprising 85% by mass of LiMn ₂ O ₄ (average particle diameter: 15 μm) as a positive electrode active material, 5% by mass of acetylene black as a conductive assistant, and 10% by mass of PVdF as a binder was prepared. An appropriate amount of N-methyl-2-pyrrolidone (NMP), which is a slurry viscosity adjusting solvent, was added to the solid content to prepare a positive electrode slurry. Next, the positive electrode slurry is applied to both sides of an aluminum foil (20 μm) as a current collector, dried and pressed, and a positive electrode having a single-side coating amount of 20.0 mg / cm ² and a double-sided thickness of 172 μm (including foil) is applied. Created.

[3. Production of negative electrode]
Artificial graphite (average particle size: 20 μm) 95% by mass as a negative electrode active material, 2% by mass of acetylene black as a conductive assistant, 2% by mass of SBR (manufactured by Zeon Corporation), CMC (manufactured by Nippon Paper Chemicals Co., Ltd. : Sunrose) A solid content of 1% by mass was prepared. An appropriate amount of ion-exchanged water, which is a slurry viscosity adjusting solvent, was added to the solid content to prepare a negative electrode slurry. Next, the negative electrode slurry is applied to both sides of a copper foil (15 μm) as a current collector, dried and pressed to produce a negative electrode with a coating amount of 5.64 mg / cm ^{2 on} one side and a thickness of 92 μm (including foil) on both sides. did.

[4. Single cell completion process]
The positive electrode produced above was cut into a 210 × 184 mm rectangular shape, and the negative electrode layer was cut into a 215 × 188 mm rectangular shape (15 positive electrodes and 16 negative electrodes). The positive electrode and the negative electrode were alternately laminated through a 219 × 191 mm separator (polyolefin microporous membrane, thickness 25 μm, porosity 55%).

A tab is welded to each of the positive electrode and the negative electrode, and the battery is completed by sealing together with an electrolyte solution in an amount shown in Table 1 below in an exterior made of an aluminum laminate film, and a urethane rubber sheet larger than the electrode area ( The laminate was sandwiched with a thickness of 3 mm), and then the laminate was further sandwiched with an aluminum plate (thickness 5 mm) to complete a nonaqueous electrolyte lithium ion secondary battery (unit cell). The urethane rubber sheet and the aluminum plate can function as pressurizing means for applying an external pressure in the battery stacking direction, and the applied external pressure is variable. The battery thus fabricated had a rated capacity of 17.7 Ah, and the ratio of the battery area to the rated capacity was 28.8 cm ² / Ah.

[5. Single cell initial charge and discharge process]
About the nonaqueous electrolyte lithium ion secondary battery (unit cell) produced as mentioned above, first, after hold | maintaining for 24 hours in the thermostat hold | maintained at 25 degreeC, the first charging / discharging process was implemented. The initial charge was a constant current charge (CC) up to 4.2 V at a current value of 0.05 CA, and then a constant voltage (CV) for a total of 25 hours. Subsequently, it hold | maintained for 96 hours in the thermostat hold | maintained at 40 degreeC. Thereafter, in a thermostatic chamber maintained at 25 ° C., discharging was performed to 2.5 V at a current rate of 1 C, and then a 10-minute rest period was provided.

[6. Battery evaluation]
The non-aqueous electrolyte lithium ion secondary battery (unit cell) produced as described above was evaluated by a charge / discharge performance test after setting the battery temperature to 45 ° C. in a thermostatic bath maintained at 45 ° C. In this charge / discharge performance test, charging was carried out at a constant current (CC) up to 4.2 V at a current rate of 1 C, and then charged at a constant voltage (CV) for 2.5 hours. Thereafter, after a 10-minute rest period, discharging was performed at a current rate of 1 C up to 2.5 V, followed by a 10-minute rest period. These were made into 1 cycle, and the charging / discharging test was implemented. The ratio of discharge after 300 cycles with respect to the initial discharge capacity was defined as the capacity maintenance rate.

  In addition, when charging / discharging in the above-mentioned “5. Initial charging process of cell” and “6. Evaluation of battery”, SOC is calculated from the voltage of the battery as needed, and a film type pressure distribution measuring system manufactured by tekscan is used. The external pressure applied in the stacking direction of the battery was monitored. The external pressure applied to the battery was changed as shown in Table 1 below when the SOC of the battery was 0 to 3% and when the SOC was 3 to 100%. In Comparative Example 3 and Comparative Example 4, the same charge / discharge test was performed without using the pressurizing means (urethane rubber sheet and aluminum plate) (that is, without applying external pressure in the battery stacking direction). did.

  From the results shown in Table 1, when a constant external pressure was applied to all SOCs, the cycle durability was temporarily improved as compared with the case where no external pressure was applied. However, this cycle durability is not sufficient. On the other hand, when the SOC is 3% or less, it is understood that the cycle durability of the battery is remarkably improved by performing charge / discharge by reducing the external pressure.

  From the above, according to the secondary battery system according to the present invention, a decrease in cycle durability in the laminated battery is suppressed, and the cycle durability of several hundred cycles required when used as a power source for electric vehicles is improved. It is shown that it is also possible.

3 Controller (SOC calculation means, control means),
4 Pressurizing device (pressurizing means),
10 Nonaqueous electrolyte secondary battery,
11 positive electrode current collector,
12 negative electrode current collector,
13 positive electrode active material layer,
15 negative electrode active material layer,
17 separator,
19 cell layer,
21 power generation elements,
25 positive current collector,
27 negative current collector,
29 Battery exterior body,
30 Excess space inside the battery exterior body,
31 Ammeter,
32 Voltmeter,
33 Relay switch,
34 External pressure sensor (external pressure detection means)
35 Auxiliary power supply,
41 restriction plate,
42 Lower plate,
43 Upper plate,
44 bolts and nuts,
45 ball screw,
46 Screw shaft,
47 Nut,
48 motor,
50 load,
51 Inverter.

Claims (11)

A positive electrode in which a positive electrode active material layer is formed on the surface of the positive electrode current collector; a negative electrode in which a negative electrode active material layer is formed on the surface of the negative electrode current collector; and a separator for holding an electrolyte solution A non-aqueous electrolyte secondary battery in which a power generation element having a single battery layer is sealed so that there is an excess space inside the exterior body together with an electrolyte containing an electrode protecting agent inside the exterior body,
Pressurizing means for applying an external pressure to the non-aqueous electrolyte secondary battery;
SOC calculating means for calculating the SOC of the non-aqueous electrolyte secondary battery;
Control means for controlling the pressurizing means based on the SOC calculated by the SOC calculating means to adjust the external pressure,
The non-aqueous electrolyte secondary battery system, wherein the control means reduces the external pressure when the SOC becomes a predetermined value or less during discharging of the non-aqueous electrolyte secondary battery. An external pressure detecting means for detecting the external pressure;
The non-aqueous electrolyte secondary battery system according to claim 1, wherein the control unit controls the pressurizing unit such that the external pressure detected by the external pressure detecting unit falls within a predetermined range. 3. The nonaqueous electrolyte secondary battery system according to claim 1, wherein the external pressure after the decrease is 0.1 kgf / cm ² or more and less than 0.4 kgf / cm ² as a pressure in the stacking direction of the power generation elements.   The non-aqueous electrolyte secondary battery system according to any one of claims 1 to 3, wherein the predetermined value is 3 to 5%.   The non-aqueous electrolyte secondary battery system according to claim 1, wherein the control unit further increases the external pressure when the SOC becomes larger than the predetermined value. The nonaqueous electrolyte secondary battery system according to claim 5, wherein the increased external pressure is 0.4 to 1.5 kgf / cm ² as a pressure in the stacking direction of the power generation elements.   The said electrode protective agent is 1 type, or 2 or more types of compounds selected from the group which consists of vinylene carbonate, vinylethylene carbonate, fluoroethylene carbonate, and difluoroethylene carbonate, The any one of Claims 1-6. Non-aqueous electrolyte secondary battery system. The electrode protective agent is represented by the following formula (1):
Where
O represents oxygen and S represents sulfur;
A, B and D each independently represent at least one group selected from the group consisting of a single bond, oxygen, sulfur, carbonyl group, thiocarbonyl group, sulfinyl group, sulfonyl group, and NR ⁵ group; In this case, R ⁵ represents at least one group selected from the group consisting of a hydrogen atom, a monovalent aliphatic hydrocarbon group, a monovalent alicyclic hydrocarbon group, and a monovalent aromatic hydrocarbon group. ,
R ¹ , R ² , R ³ and R ⁴ each independently represents a single bond or a divalent aliphatic hydrocarbon group,
The nonaqueous electrolyte secondary battery system of any one of Claims 1-7 which is 1 type, or 2 or more types of cyclic sulfonate ester represented by these. The power generation element has a configuration in which a plurality of unit cell layers are stacked,
The non-aqueous electrolyte secondary battery system according to claim 1, wherein the pressurizing unit applies the external pressure in a stacking direction of the power generation elements of the non-aqueous electrolyte secondary battery. The value of the ratio of the battery area to the rated capacity (projected area of the battery including the battery outer package) is 5 cm ² / Ah or more, and the rated capacity is 3 Ah or more. The nonaqueous electrolyte secondary battery system described in 1.   The non-aqueous electrolyte secondary according to any one of claims 1 to 10, wherein the active material layer has a rectangular shape, and an aspect ratio of the electrode defined as an aspect ratio of the active material layer is 1 to 3. Battery system.